The positioning and deployment of medical implants is a common often-repeated procedure of modern medicine. Medical implants may be used for innumerable medical purposes including the reinforcement of recently re-enlarged lumens and the replacement of ruptured vessels. These implants may be delivered by securing them to the distal end of a delivery device, positioning the distal end of the device near a target delivery site, and then deploying the implant from the device to its desired position. The implant may be deployed by inflating the distal end of the device or through other forces that urge the implant from the device's distal end. When the implant has been coated this coating is susceptible to being damaged or completely removed from the implant during the deployment process—an unwanted result.
The mechanical process of deploying the implant often exerts significant shearing and adhesional forces on and against the surface of the coating of the implant. These forces can strip, damage or otherwise deplete the amount of coating on the implant. When the amount of coating is depleted the implant's effectiveness may be compromised and additional risks may be inured into the procedure. For example, when the coating of the implant includes a therapeutic, if some of the coating were removed during deployment, the therapeutic may no longer be able to be administered to the target site in a uniform and homogenous manner. Thus, some areas of the target site may receive high quantities of therapeutic while others may receive low quantities of therapeutic. Similarly, if the therapeutic is ripped from the implant it can reduce or slow down the blood flowing past it, thereby, increasing the threat of thrombosis or, if it becomes dislodged, the risk of embolisms.
The delivery of expandable stents, stent grafts, and aneurysm coils are specific examples of medical procedures that involve the deployment of coated implants. Expandable stents are tube-like medical devices designed to support the inner walls of a lumen within the body of a patient. These stents are typically positioned within a lumen of the body and, then, expanded to provide internal support for the lumen. They may be self-expanding or, alternatively, may require external forces to expand them. In either case they are typically deployed through the use of a catheter of some kind. These catheters will typically carry the stent at their distal end.
Because of the direct contact of the stent with the inner walls of the lumen, stents have been coated with various compounds and therapeutics to enhance their effectiveness. These coatings may, among other things, be designed to facilitate the acceptance of the stent into its applied surroundings and to facilitate the delivery of therapeutic to the target site. When this coating is haphazardly applied or has somehow been removed during the stent's manufacture or delivery the stent's effectiveness can be compromised.
In certain circumstances faulty or ineffectively deployed stents can require the removal and reinsertion of the stent through a second medical procedure. For example, as the balloon at the distal end of the stent is inflated, to expand and position the stent, frictional shear forces are created between the surface of the catheter and the stent coating. These frictional surface shear forces, as well as the adhesional forces between the coating and the stent, act to tear away or unevenly redistribute the stent coating. Thus, the physical forces used to deliver the stent can create an abating result that reduces the overall effectiveness of a deployed coated stent.